The present invention relates to a rotating hydraulic distributor for hydraulic actuating systems, more particularly for power assisted systems of automotive vehicles, of the type comprising two axially adjacent members adapted to rotate one relative to the other over a limited angular range under the action of a control means, each said member comprising at least one aperture opening on its face directed toward the other member, the adjacent lateral edges of associated apertures of said members mutually cooperating, during relative rotation of said members so as to define a modulable elongated fluid flow passage between said apertures.
Historically, rotating hydraulic distributors have been developed initially under the form of an elongated cylindrical rotor arranged coaxially within a sleeve, both said members have axially extending grooves opening at the level of the interface between said two members and selectively mutually cooperating to define selective fluid flow paths in the distributor while producing a differential pressure variation for actuation of an hydraulic assistance motor. In such a class of distributor, a progressive exposure or closure of the groove establishes modulable fluid flow passages having well determined lateral dimensions by reasons of the parallelism of the (axial) edges of the grooves. However, due to quite important noise problems occurring at the beginning of the opening of the fluid flow passages, the distributor manufacturers have been led to provide said closing lateral edges with chamfers which permit to achieve a more progressive opening (or closure) of the fluid flow passage. Such a technique is disclosed in the European patent application Ser. No. 0,012,043 (DBA).
For reasons of reduction of overall dimensioning of the rotating hydraulic distributors and in order to simultaneously permit a better flexibility in the functions achieved by the rotating distributor, the Applicant has developed rotating hydraulic distributors comprising two axially adjacent members according to the so-called technique of the "star-shaped" rotor, such as disclosed in U.S. Pat. No. 4,459,897 issued July 17, 1984 in the name of the Applicant company, the content of which is supposed integrated here for reference. Said technique has therebetween led to interesting developments by taking into account the fact that the shape of the chamfers of the closing lateral edges of the different arms of the star-shaped rotor can be used to control successive portions of the characteristic curve input torque/actuating fluid pressure of the distributor. Such a technique is disclosed in U.S. Pat. No. 4,310,024 in the name of the Applicant company.
However, contrary to the hydraulic distributors of the type embodying a cylindrical rotor and a peripheral sleeve, the relative angular displacement of said two axially adjacent members raises problems of angular misalignment between the cooperating lateral edges of each member by reason of the variations of the radii between the base (adjacent the rotation center) and the outer end (more remote from said rotation center) of said cooperating edges. Thus, if, in the rest position of the distributor, the two adjacent cooperating edges belonging respectively to the first and second rotating members extend parallel to each other to provide therebetween a fluid flow passage having a substantially rectangular shape, as a result of a relative rotation between said distributor members, for instance for restricting said fluid flow passage, the fluid flow passage will adopt the shape of a wedge, with a width (as taken in the peripheral direction) varying in dependence of the radial length extension of the passage. Resulting therefrom is an effective loss of control of the optimum dimensions of the fluid flow passage together with the apparition of a phenomenon of fluid flow recirculation in the radial direction, which induces intempestive pressure drops, perceptible noises and even an intempestive instability in operation of the distributor. Said phenomena are still increased when providing the closing edges with chamfers, e.g. a single chamfer or more often with simple or successive step-shaped chamfer formations.